Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old June 15th 20, 03:10 PM posted to sci.electronics.repair
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Default Panasonic microwave, blown inverter board transformer

It is all in accordance with what you want.

An "inverter" microwave modulates the output of the magnetron directly. So, 50% setting means the magnetron is putting out 50% of its full capacity, but all of the time. With a conventional microwave, that is achieved by running the magnetron in duty/rest cycles. 100% for 50% of the time 0% for 50% of the time. Inverter-based microwaves become far more flexible and therefore far more useful.

Re Reliability: Our present Panasonic (inverter) is about 6 years old and gets moderate use. It replaced a 16 year old multi-voltage BEAC we purchased in Saudi, that is now still in minimal use by a neighbor in his garage workshop. We keep our devices clean, make sure they get enough air circulation, and, heaven forfend, even clean the vents regularly!

Basic care-and-feeding is becoming a lost art.

Peter Wieck
Melrose Park, PA


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Old June 15th 20, 07:17 PM posted to sci.electronics.repair
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Default Panasonic microwave, blown inverter board transformer

On 2020/06/08 7:44 p.m., Mike S wrote:
On 6/8/2020 9:04 AM, wrote:
OK. On the one hand:

Purchase new Board: US$25 + shipping
Install New Board: 2 hours work

It all works: All good!

Magnetron is bad: Purchase new Magnetron for US$65 + shipping
Install new Magnetron: 2 hours work.

It wall works: 4 hours + US$90 + shipping.

On the other hand, a brand new 1,000 watt microwave: US$150, complete
with warranty.

I admire your wish to reduce landfill, but I have to wonder at the
investment in a 10 year old device that is heavily used by your own
description.

Peter Wieck
Melrose Park, PA

Farberware Classic 1.1 cu. ft .1000-Watt Microwave Oven $99.99
Farberware Classic 0.9 cu. ft. 900-Watt Microwave Oven $89.99

https://www.hsn.com/shop/50-99-range...es/ho0514-6664



The question is, how long would these MWs last under the same usage as
the original Panasonic? I suspect perhaps 5 years...so repairing a
machine that lasted 10 years, might cost $100 - and give it another ten
years. Vs. replacing it with a cheaper design that may last 1/2 the
time? Is that really a better deal? Plus you have saved landfill.

John :-#)#
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Old June 15th 20, 08:08 PM posted to sci.electronics.repair
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Default Panasonic microwave, blown inverter board transformer

On Mon, 8 Jun 2020 00:02:34 +0100, Andrew wrote:

Hi, I have an NN-A554W and the transformer on the inverter board has
blown. Microwave wouldn't start cooking so I ran it for a moment with
the cover off, transformer did a light and smoke display and now it
smells like fireworks.


Impressive. I know how you feel:
http://www.learnbydestroying.com/jeffl/pics/drivel/#burned-yam.jpg
That's what happened when I cooked a yam (potatoe) for 16 minutes
instead of 6 minutes. It was glowing bright red inside just before I
opened the door. The inside of my Panasonic NN-S533WF (Sensor 1300w)
microwave oven changed from white to yam colored. I tried to clean
it, but the yam color is permanently baked into the paint. The S/N
label says made in 2003. I think I received it as a present in 2005,
making it 15 years old. It works as well today as it did in 2005 with
no change in output level. That's one of the benefits of an inverter
oven.

I made sure the magnetron was discharged and between the two connections
I am getting 0 ohms, but I only have a basic multimeter. Between those
and the casing is open.


Try measuring again with a much better ohmmeter or preferably an ESR
meter, which will measure resistances below 1 ohm. The two terminals
on the magottron are the filament wires. Less than 1 ohm is typical
and is easily mistaken for a short circuit.
"Magnetron Test for Opens, shorts or Insufficient Power"
https://www.microwavespecialties.com/pdfs/E10-2010-06%20Mag%20Test%20Bulletin.pdf
The instructions are for a commerical oven, which may have more than
one magnetron inside, but the methods are the same for a home
microwave oven with only one magnetron.

This microwave is at least 10 years old with a lot of use, so how likely
is it that the transformer has just gone by itself vs the magnetron or
the small mains input board dying and taking the transformer with it?


Near zero. I haven't repaired too many microwave ovens and only one
inverter oven. Mostly, what I find are (in order of frequency):
1. Blown high voltage diodes.
2. Blown high voltage capacitor.
3. Blown thermal protection fuse.
4. Filthy and intermittent door interlock switch.
5. Low magentron output or dead magnetron.
I would guess I've fixed about 20 mw ovens and have yet to see a blown
high voltage transformer. If the enamel coating on the torroid are
discoulored from overheating, you might have a problem with the
transformer. If it looks normal, it's something else.

You might want to try searching on YouTube for videos on how to
diagnose and repair microwave ovens. This looks like a good start:
https://www.youtube.com/watch?v=hBJJU4ZRh7U

The other thing is that the part number of the inverter/transformer
board is A6645M304GP, and the magnetron is a 2M236-M42. A lot of other
models seem to use boards that look identical, but not exactly the same
part number. For example I have found a site saying that this magnetron
can be used with an A66454T05AP or F66454T07AP board, which do look the
same as mine, so are they just a different revision or something or are
the differences going to be bigger?


What you're seeing are differences in part number because the
manufacturer sourced their magnetron from multiple (Chinese) sources.
Each source has a different part number, but are functionally and
mechanically identical. The NN-A554W is a 1000 watt oven, so any 1000
watt magnetron that mechanically fits is likely to work.

Even if I need exactly the same board, it looks like I could be chasing
a part that would work in many different models, even different brands,
if only I knew which one to look for (it seems there are no parts for my
model).


No parts? Google is your friend:
https://www.google.com/search?q=NN-A554W+oven+parts
Hmmm... are you in the UK? The Panasonic model number seems to be a
UK only 230VAC oven?

Am worried about replacing it and having the new one get instantly blown
up though.


Well, if you want an exact replacement, it would helpful if you would
supply the full model number. Is it NN-A554WB or NN-A554WF ?

If you have no clue what you're doing, and are lacking in basic test
equipment, I would recommend:
1. Checking the magnetron with an ohms guesser.
2. If ok, replace the Hi-V diodes and Hi-V capacitor.
3. If that doesn't fix it, don't replace the magnetron. Instead by a
replacement inverter board. It's one of these:
https://www.kitchenwareonline.com/panasonic-microwave-oven-hv-inverter-m3ffzz000bp-c2x13938345
https://www.kitchenwareonline.com/panasonic-hv-inverter-for-microwave-ovens-z606yba00gp-c2x15619538
4. If that doesn't fix it, it MIGHT be the magnetron, but I doublt
it. Magnetrons usually fade away slowly, where cooking takes longer
and longer, until it doesn't cook. It does not die suddenly or belch
fire. If you bought a replacement board, you've probably spend more
on the repair than the oven is worth. I suggest you cut your losses
and just buy a new oven.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old June 15th 20, 08:26 PM posted to sci.electronics.repair
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Default Panasonic microwave, blown inverter board transformer

The longevity of any given appliance is a factor. But, in one's choice of appliances, longevity is only one (1) factor. If one looks at the life-cycle cost, the factors a

a) Cost to produce, market, transport and sell.
b) Cost of energy used over the life of the appliance (and, technically, the source of that energy).
c) Cost of disposal when 'used up'.

Then, there are wearing parts: hinges & latches, microwave safe internal finishes, bearings and so forth. Investing in repair parts might not give that further ten years.

So, if one assumes that the typical microwave lasts around ten years, and is in actual use for (low end for this purpose) one full hour per week, that comes to 520 hours of operation. A magnetron tube is about 65% efficient these days. Assume all microwaves are a (mere) 700 watts. Assume the US national average cost pr KWH of $0.1331. The equation looks like this:

((700/0.65) x 520)/1,000)=560. 560 x 0.1331 = 74.536. So, it will use $74.54 in electricity in those 10 years at that rate. A modern inverter stands to use, on average, 50% less energy. So use $37 as the 'advantage' per ten years to the inverter technology.

I dunno... It has been my experience that modern microwaves are largely made of parts made by robots, assembled mostly by robots, tested by robots and (maybe) visually inspected and packed by a exceedingly bored human.

https://www.midea-group.com/About-Us...hen-appliances

http://www.midea-gy.com/files/images/shebei/02.jpg

Chances for human error are minuscule. Finishes are far better. Parts variability is far less. And so on. As cheaply made and looking as these things might feel, with proper care and feeding, there is no reason why that $89 dollar device might not last that 10 years and beyond.

Fully agreed on the landfill - we are privileged that most scrap metal from our township is recycled to Acelor Mittal:

https://usa.arcelormittal.com/our-op...ng/coatesville Which has been in continuous, uninterrupted operation (including wars, depressions, holidays and so forth) since 1810.

It is a process.

Peter Wieck
Melrose Park, PA
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Old June 17th 20, 08:41 AM posted to sci.electronics.repair
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Default Panasonic microwave, blown inverter board transformer

wrote:
It is all in accordance with what you want.

An "inverter" microwave modulates the output of the magnetron directly.
So, 50% setting means the magnetron is putting out 50% of its full
capacity, but all of the time. With a conventional microwave, that is
achieved by running the magnetron in duty/rest cycles. 100% for 50% of
the time 0% for 50% of the time. Inverter-based microwaves become far
more flexible and therefore far more useful.

Re Reliability: Our present Panasonic (inverter) is about 6 years old


well, panasonic does make a decent microwave oven, so this is probably the
cadillac of anything with an inverter in it. I have a hand me down
inverter panasonic. Seems to work fine, I just use the quick minute button
for anything but defrosting stuff. I still have no idea what a baked
potato button is supposed to do or why I'd want a power level of 2/10 or
anything goofy like that. My favorite interface was on the Tappan ovens
with a timer with two timing ranges, a cook/defrost switch and start and
stop buttons. The design was pure genius, and hasn't been surpassed to
this day. I also keep a 1981 samsung microwave in the museum. It has a
whopping 20 screws just to keep the plastic window and shield in the door.
No way any part on a $89 medea special will mechanically outlast this
thing.

and gets moderate use. It replaced a 16 year old multi-voltage BEAC we
purchased in Saudi, that is now still in minimal use by a neighbor in
his garage workshop. We keep our devices clean, make sure they get
enough air circulation, and, heaven forfend, even clean the vents
regularly!

Basic care-and-feeding is becoming a lost art.


I do the open up and deep clean and oil fan bearings every so many years,
but this is not something a normal consumer could or should do. BWT, the
fans in modern robo-build microwaves are truly puny garbage. I bent she
shaft of one just trying to remove the fan blades. No joke. They're really
engineered the quality out of these things.


Peter Wieck
Melrose Park, PA

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Old June 17th 20, 08:55 AM posted to sci.electronics.repair
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Default Panasonic microwave, blown inverter board transformer

Jeff Liebermann wrote:
On Mon, 8 Jun 2020 00:02:34 +0100, Andrew wrote:

Hi, I have an NN-A554W and the transformer on the inverter board has
blown. Microwave wouldn't start cooking so I ran it for a moment with
the cover off, transformer did a light and smoke display and now it
smells like fireworks.


Impressive. I know how you feel:
http://www.learnbydestroying.com/jeffl/pics/drivel/#burned-yam.jpg
That's what happened when I cooked a yam (potatoe) for 16 minutes
instead of 6 minutes. It was glowing bright red inside just before I
opened the door. The inside of my Panasonic NN-S533WF (Sensor 1300w)
microwave oven changed from white to yam colored. I tried to clean
it, but the yam color is permanently baked into the paint. The S/N
label says made in 2003. I think I received it as a present in 2005,
making it 15 years old. It works as well today as it did in 2005 with
no change in output level. That's one of the benefits of an inverter
oven.


Lol, I've wondered about the "sensor" in these things. I know can't be
related to any sort of device that measures anything. Must be marketing
speak or a weirdly translated word.

I made sure the magnetron was discharged and between the two connections
I am getting 0 ohms, but I only have a basic multimeter. Between those
and the casing is open.


Try measuring again with a much better ohmmeter or preferably an ESR
meter, which will measure resistances below 1 ohm. The two terminals
on the magottron are the filament wires. Less than 1 ohm is typical
and is easily mistaken for a short circuit.
"Magnetron Test for Opens, shorts or Insufficient Power"
https://www.microwavespecialties.com/pdfs/E10-2010-06%20Mag%20Test%20Bulletin.pdf
The instructions are for a commerical oven, which may have more than
one magnetron inside, but the methods are the same for a home
microwave oven with only one magnetron.

This microwave is at least 10 years old with a lot of use, so how likely
is it that the transformer has just gone by itself vs the magnetron or
the small mains input board dying and taking the transformer with it?


Near zero. I haven't repaired too many microwave ovens and only one
inverter oven. Mostly, what I find are (in order of frequency):
1. Blown high voltage diodes.
2. Blown high voltage capacitor.
3. Blown thermal protection fuse.
4. Filthy and intermittent door interlock switch.
5. Low magentron output or dead magnetron.
I would guess I've fixed about 20 mw ovens and have yet to see a blown
high voltage transformer. If the enamel coating on the torroid are
discoulored from overheating, you might have a problem with the
transformer. If it looks normal, it's something else.

You might want to try searching on YouTube for videos on how to
diagnose and repair microwave ovens. This looks like a good start:
https://www.youtube.com/watch?v=hBJJU4ZRh7U

The other thing is that the part number of the inverter/transformer
board is A6645M304GP, and the magnetron is a 2M236-M42. A lot of other
models seem to use boards that look identical, but not exactly the same
part number. For example I have found a site saying that this magnetron
can be used with an A66454T05AP or F66454T07AP board, which do look the
same as mine, so are they just a different revision or something or are
the differences going to be bigger?


What you're seeing are differences in part number because the
manufacturer sourced their magnetron from multiple (Chinese) sources.
Each source has a different part number, but are functionally and
mechanically identical. The NN-A554W is a 1000 watt oven, so any 1000
watt magnetron that mechanically fits is likely to work.

Even if I need exactly the same board, it looks like I could be chasing
a part that would work in many different models, even different brands,
if only I knew which one to look for (it seems there are no parts for my
model).


No parts? Google is your friend:
https://www.google.com/search?q=NN-A554W+oven+parts
Hmmm... are you in the UK? The Panasonic model number seems to be a
UK only 230VAC oven?

Am worried about replacing it and having the new one get instantly blown
up though.


Well, if you want an exact replacement, it would helpful if you would
supply the full model number. Is it NN-A554WB or NN-A554WF ?

If you have no clue what you're doing, and are lacking in basic test
equipment, I would recommend:
1. Checking the magnetron with an ohms guesser.
2. If ok, replace the Hi-V diodes and Hi-V capacitor.
3. If that doesn't fix it, don't replace the magnetron. Instead by a
replacement inverter board. It's one of these:
https://www.kitchenwareonline.com/panasonic-microwave-oven-hv-inverter-m3ffzz000bp-c2x13938345
https://www.kitchenwareonline.com/panasonic-hv-inverter-for-microwave-ovens-z606yba00gp-c2x15619538
4. If that doesn't fix it, it MIGHT be the magnetron, but I doublt
it. Magnetrons usually fade away slowly, where cooking takes longer
and longer, until it doesn't cook. It does not die suddenly or belch
fire. If you bought a replacement board, you've probably spend more
on the repair than the oven is worth. I suggest you cut your losses
and just buy a new oven.


I'd follow these steps too, but I also have the test equipment for doing
so, but OP says they have an inverter microwave. That should scratch the
#2s off the list, which is really easy for for a traditional half-doubler
microwave oven. They have no way to test the HV section safely. Microwaves
are truly the most dangerous electronic appliances to play with.
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Old June 17th 20, 01:34 PM posted to sci.electronics.repair
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Default Panasonic microwave, blown inverter board transformer

Cydrome Leader wrote:

Lol, I've wondered about the "sensor" in these things. I know can't be
related to any sort of device that measures anything. Must be marketing
speak or a weirdly translated word.


I don't think the "sensor" is a gimmick.

From what I ran across somewhere, it's like a humidity or moisture
measurement and really did/does work. I just had a 16~17 year old GE
over-the-range type that went out that used sensor cooking and now using a
$99 counter top model (1250W Magic Chef) that doesn't, I miss it.

I would of replaced the GE with a current model but it's a 2 man job and
with ye old pandemic, I figured the $99 special will suffice for now until
an assistant is found. What's odd with the break down is the keypad doesn't
work and it's not the keypad or ribbon cable.

About a month before I noticed the 3-6-9 buttons wouldn't do anything but
all the others were fine. Then one early morning, ComEd (local power
company) cut the power for about 10 minutes which reset the clock back to
the blinking 12 (actually I think it scrolls "Press clock to set time") and
that was that. No more workie. It does boot, plug it in, you get the beep
and even the "GE brings great things to life" scrolls on the display.

Everywhere I checked for parts (figured a new/used control panel) ended up
the same "Not in stock - No Longer Available".

Disappointing.

-bruce

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Old June 18th 20, 01:50 AM posted to sci.electronics.repair
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Default Panasonic microwave, blown inverter board transformer

On Wed, 17 Jun 2020 06:55:26 +0000 (UTC), Cydrome Leader
wrote:

Jeff Liebermann wrote:
On Mon, 8 Jun 2020 00:02:34 +0100, Andrew wrote:

Hi, I have an NN-A554W and the transformer on the inverter board has
blown. Microwave wouldn't start cooking so I ran it for a moment with
the cover off, transformer did a light and smoke display and now it
smells like fireworks.


Impressive. I know how you feel:
http://www.learnbydestroying.com/jeffl/pics/drivel/#burned-yam.jpg
That's what happened when I cooked a yam (potatoe) for 16 minutes
instead of 6 minutes. It was glowing bright red inside just before I
opened the door. The inside of my Panasonic NN-S533WF (Sensor 1300w)
microwave oven changed from white to yam colored. I tried to clean
it, but the yam color is permanently baked into the paint. The S/N
label says made in 2003. I think I received it as a present in 2005,
making it 15 years old. It works as well today as it did in 2005 with
no change in output level. That's one of the benefits of an inverter
oven.


Lol, I've wondered about the "sensor" in these things. I know can't be
related to any sort of device that measures anything. Must be marketing
speak or a weirdly translated word.


It's a humidity sensor. When whatever you're cooking gets hot enough
to vaporize water, the "sensor" detects the water vapor and shuts off
the oven, usually after a short delay. The alleged advantage is that
you don't need to enter the cooking time or power level, but you do
need to enter the type of food:
https://www.youtube.com/watch?v=__tYa70kRHY
I've only used the sensor feature a few times. No opinion on whether
it's useful, or yet another useless feature.

I'd follow these steps too, but I also have the test equipment for doing
so, but OP says they have an inverter microwave. That should scratch the
#2s off the list, which is really easy for for a traditional half-doubler
microwave oven. They have no way to test the HV section safely. Microwaves
are truly the most dangerous electronic appliances to play with.


If you don't know what you're doing, don't have sufficient experience,
can't follow advice, and are afraid of high voltage, perhaps you
really shouldn't be fixing microwave ovens?

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old June 18th 20, 06:11 AM posted to sci.electronics.repair
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Default Panasonic microwave, blown inverter board transformer

wrote:
Cydrome Leader wrote:

Lol, I've wondered about the "sensor" in these things. I know can't be
related to any sort of device that measures anything. Must be marketing
speak or a weirdly translated word.


I don't think the "sensor" is a gimmick.

From what I ran across somewhere, it's like a humidity or moisture
measurement and really did/does work. I just had a 16~17 year old GE
over-the-range type that went out that used sensor cooking and now using a
$99 counter top model (1250W Magic Chef) that doesn't, I miss it.


Say there is a moisture detector in ther sniffing the air being pulled
from the cavity. It doesn't prevent a frozen pot pie from burning, it
doesn't prevent anything from overcooking. It doesn't seem to know when a
frozen sausage is transitioning from thawing to outright cooking. I really
have no idea what it's doing. It's too mysterious to take seriously.
Really old microwaves sometimes had the temperature probe- that made
sense, assuming you were into cooking a turkey in the microwave oven for
30 minutes.

Say it's real. Do the just modulate the cooing duty cycle? It doesn't seem
to speed up or slow anything down, ot at least I've not found a mode that
isn's still time based.

What were the delicious things you could pull off with the sensor as sous
chef that just don't work with the magic chef?

I would of replaced the GE with a current model but it's a 2 man job and
with ye old pandemic, I figured the $99 special will suffice for now until
an assistant is found. What's odd with the break down is the keypad doesn't
work and it's not the keypad or ribbon cable.

About a month before I noticed the 3-6-9 buttons wouldn't do anything but
all the others were fine. Then one early morning, ComEd (local power
company) cut the power for about 10 minutes which reset the clock back to
the blinking 12 (actually I think it scrolls "Press clock to set time") and
that was that. No more workie. It does boot, plug it in, you get the beep
and even the "GE brings great things to life" scrolls on the display.

Everywhere I checked for parts (figured a new/used control panel) ended up
the same "Not in stock - No Longer Available".


Any parted out ones on ebay? No real need for "new" as long as it works.

Disappointing.


I was approached with a friend asking how to fix their above range
microwave oven too. I want to help, but until they can read me the model #
off the door, I can't do much with suggestions on what the next move is.


-bruce



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